Oklahoma, Kansas and Nebraska -- states that are part of what's known as Tornado Alley -- had no tornadoes this year as of last week; typically, the three would have seen nearly 50 tornadoes by the end of April.

This year is the latest start to tornado season in Oklahoma since the National Oceanic and Atmospheric Administration began keeping records on severe storms.

It's also only the fourth time in recorded history that Kansas has gone all of April without a tornado.

But on Tuesday there were reports of 18 tornadoes across these states -- one in Oklahoma, 12 in Kansas and five in Nebraska.

Survey teams from the National Weather Service will need to confirm that these were indeed tornadoes. Until then, such reports are all preliminary.

"Frequent shots of cold air from repeated Arctic blasts have confined the warm and humid air needed for severe weather to the Southeast this spring, but longer days and an increasing sun angle are finally starting to win the battle against the cold," CNN meteorologist Brandon Miller said, explaining the uptick in storm activity in the Plains.

More than 1 million people in Missouri and Kansas are at a moderate risk for severe storms.

"Storms today are forecast to be more linear in nature, which will lead to more damaging winds than tornadoes. Yesterday the storms were (isolated), which leads to more tornadoes," CNN meteorologist Dave Hennen said.

Northeast Kansas and northwest Missouri will be at moderate risk mostly for severe winds and hail.

An enhanced risk for severe storms stretches from Western Oklahoma to northern Missouri -- including Wichita, Kansas, and Kansas City, Missouri -- and an area from central Oklahoma to central Kansas will be more at risk for tornadoes than any other location Wednesday.

With such a small area forecast for tornadoes, tornado chasers will likely all try to converge on the same storms, creating traffic jams and other dangers.

Just because the forecast for tornadoes is a smaller area doesn't mean that a tornado will not form anywhere else in the overall marginal risk area, which stretches from the US-Mexico border in Texas to the Great Lakes. But the area covering Oklahoma, Missouri and Iowa is more likely to see damaging storms.

Thursday the risk will continue but will push a little farther east.

Parts of Iowa and Missouri will be under the gun again, with an enhanced risk for severe storms Thursday afternoon. A slight risk of storms is forecast from Dallas to near Chicago.